1. Field of the Invention
The present invention relates to photodiode arrays and image pickup devices. More specifically, the invention relates to a photodiode array and an image pickup device that have a light-receiving sensitivity in a wavelength region extending to the near infrared region at the long-wavelength side.
2. Description of the Related Art
Group III-V compound semiconductors have received attention as compound semiconductors having band gap energy suitable for wavelengths in the near infrared region or in a region of still longer wavelengths, and have been being researched and developed. For example, Marshall J. Cohen and Gregory H. Olsen disclose a night-vision camera receiving natural light from space (“Near-IR imaging cameras operate at room temperature”, LASER FOCUS WORLD, June 1993, pp. 109-113). The night-vision camera includes a photodiode array including photodiodes arranged on an InP substrate. The photodiode includes an InGaAs absorption layer lattice-matching with InP. The use of such a photodiode array allows images to be picked up with natural light, but not artificial lighting, even during the night or in rain.
If bright light enters the field of view of the night-vision camera when it forms an image with a relatively low-intensity incident light, however, halation occurs and images are not formed until carriers are removed from photodiode. When, for example, the brightness varies largely during image pickup of a motion picture, the night-vision camera easily comes into a state where it cannot form images. It is undesirable that a state where images cannot be formed arises in an image pickup device (sensor) for the near infrared region, from which various applications are expected. This problem should be overcome.
In addition, it is difficult that the night-vision camera forms a smooth motion picture. The silicon IC (Integrated Circuit) in which the driving circuit of the night-vision camera is to be formed limits the capacity to be provided and accordingly it takes a long time to sweep out the accumulated carriers. Hence, the frequency of the output of image forming signals is limited, and smooth motion pictures cannot be formed.